The present invention relates to a system utilizing a temperature signal from a total air temperature probe for determining outside or ambient air temperature, and controlling the total air temperature (TAT) probe heaters to avoid excess heating, which reduces product life. The determining of the outside air temperature is preferably carried out with tile processor of a xe2x80x9csmartxe2x80x9d air data sensing probe.
At the present time, total air temperature (TAT) probes or sensors are used for providing temperature inputs when the aircraft is in flight. The TAT probes, which extend into the airflow, are heated for anti-icing purposes. When the aircraft is on the ground, where there is little or no airflow, the heaters will raise the temperature of the TAT probe so directly obtaining a valid temperature signal from a temperature sensing element in the probe is not possible. When the aircraft is in flight, this is not an issue, because of the cooling effect of the airflow past the probe and sensing-element.
At the present time, outside air temperature of an aircraft on the ground is determined with a separate sensor or through manual means, such as direct voice communication with an air controller, and is used for engine settings, and other inputs prior to take off. With the need for reducing overall weight of !an aircraft, not requiring a separate outside air temperature sensor is important. When the need for manual input is eliminated pilot workload is reduced, which is desirable. Further, reducing the maximum temperature of the total air temperature probe will increase the life of the probe.
The present invention in one aspect relates to operation of a total air temperature (TAT) probe. One aspect of the invention is to use a processor on the aircraft to receive total air temperature inputs from a temperature sensing element, estimate the outside air temperature and control the maximum temperature that the TAT probe reaches when on the ground, by cycling the heater on the total temperature probe mounting the sensing element on and off, and sensing changes in the indicated temperature when the heater is turned off.
The cooling rate of the probe is determined by how quickly the temperature indication or signal from the total air temperature sensing element decays or decreases when the heater used for deicing the TAT probe is turned off. This rate of change of temperature is sensed by the sensing element in the probe, and since it is a function of the outside air temperature, it may be used to provide an accurate outside air temperature indication.
A second method for determining the outside air temperature is to heat the probe to a selected temperature, shut off the heater and sample the output signal of the temperature sensing element in the probe until the indicated temperature stabilizes, that is, until the temperature signal does not change more than a selected value during a selected time period. The outside air temperature thus is no longer causing significant cooling of the probe and the signal provided indicates the actual outside air temperature.
Predicting the outside temperature based on cooling rate is faster, but is also influenced by environmental factors, such as wind. Both methods are used together for readings of increased accuracy.
These derived indications of outside air temperature can then be used for various inputs, including engine settings and the like. Also, the heaters for the TAT probe can be turned on periodically to insure that the probe remains ice free at all times.
Another aspect of the invention is to control the heaters for the TAT probes using the processor on a smart angle of attack and pressure sensor probe (a smart probe), rather than using separate on-board computers.